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Buggy multiplication, but overall the jit seems to work

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Spencer Tipping 2017-03-12 12:42:36 -06:00
parent bd6a2a1254
commit 1766ca26ad
3 changed files with 307 additions and 2 deletions
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180
README.md
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@ -332,7 +332,8 @@ movsd %xmm2, 24(%rdi) // b.i = %xmm2
// Step 2: add register A to register B
movpd (%rdi), %xmm0 // %xmm0 = (a.r, a.i)
addpd %xmm0, 16(%rdi) // (b.r, b.i) += %xmm0
addpd %xmm0, 16(%rdi) // %xmm0 += (b.r, b.i)
movpd %xmm0, 16(%rdi) // (b.r, b.i) = %xmm0
```
The multiplication code isn't optimized for the squaring-a-register use case;
@ -340,7 +341,8 @@ instead, I left it fully general so we can use it as a template when we start
generating machine code.
### JIT mechanics
Rather than compiling a real language, let's just get a basic JIT setup.
Before we compile a real language, let's just get a basic code generator
working.
```c
// jitproto.c
@ -405,3 +407,177 @@ f(7) = 7
f(8) = 8
f(9) = 9
```
#### Generating MandelASM machine code
This is where we start to get some serious mileage out of the Intel manuals. We
need encodings for the following instructions:
- `f2 0f 11`: `movsd reg -> memory`
- `f2 0f 10`: `movsd memory -> reg`
- `f2 0f 59`: `mulsd reg <- reg` (**NB:** arg order is opposite of `addsd`)
- `f2 0f 58`: `addsd reg -> reg`
- `f2 0f 5c`: `subsd reg -> reg`
- `66 0f 11`: `movpd reg -> memory` (technically `movupd` for unaligned move)
- `66 0f 10`: `movpd memory -> reg`
- `66 0f 58`: `addpd memory -> reg`
##### The gnarly bits: how operands are specified
Chapter 2 of the Intel manual volume 2 contains a roundabout, confusing
description of operand encoding, so I'll try to sum up the basics here.
(**TODO**)
For the operators above, we've got two ModR/M configurations:
- `movsd reg <-> X(%rdi)`: mod = 01, r/m = 111, disp8 = X
- `addsd reg -> reg`: mod = 11
At the byte level, they're written like this:
```
movsd %xmm0, 16(%rdi) # f2 0f 11 47 10
# modr/m = b01 000 111 = 47
# disp = 16 = 10
addsd %xmm3, %xmm4 # f2 0f 58 e3
# modr/m = b11 100 011 = e3
```
##### A simple micro-assembler
```h
// micro-asm.h
#include <stdarg.h>
typedef struct {
char *dest;
} microasm;
// this makes it more obvious what we're doing later on
#define xmm(n) (n)
void asm_write(microasm *a, int n, ...) {
va_list bytes;
int i;
va_start(bytes, n);
for (i = 0; i < n; ++i) *(a->dest++) = (char) va_arg(bytes, int);
va_end(bytes);
}
void movsd_reg_memory(microasm *a, char reg, char disp)
{ asm_write(a, 5, 0xf2, 0x0f, 0x11, 0x47 | reg << 3, disp); }
void movsd_memory_reg(microasm *a, char disp, char reg)
{ asm_write(a, 5, 0xf2, 0x0f, 0x10, 0x47 | reg << 3, disp); }
void movsd_reg_reg(microasm *a, char src, char dst)
{ asm_write(a, 4, 0xf2, 0x0f, 0x11, 0xc0 | src << 3 | dst); }
void mulsd(microasm *a, char src, char dst)
{ asm_write(a, 4, 0xf2, 0x0f, 0x59, 0xc0 | src << 3 | dst); }
void addsd(microasm *a, char src, char dst)
{ asm_write(a, 4, 0xf2, 0x0f, 0x58, 0xc0 | dst << 3 | src); }
void subsd(microasm *a, char src, char dst)
{ asm_write(a, 4, 0xf2, 0x0f, 0x5c, 0xc0 | dst << 3 | src); }
void movpd_reg_memory(microasm *a, char reg, char disp)
{ asm_write(a, 5, 0x66, 0x0f, 0x11, 0x47 | reg << 3, disp); }
void movpd_memory_reg(microasm *a, char disp, char reg)
{ asm_write(a, 5, 0x66, 0x0f, 0x10, 0x47 | reg << 3, disp); }
void addpd_memory_reg(microasm *a, char disp, char reg)
{ asm_write(a, 5, 0x66, 0x0f, 0x58, 0x47 | reg << 3, disp); }
```
##### Putting it all together
Now that we can write assembly-level stuff, we can take the structure from the
prototype JIT compiler and modify it to compile MandelASM.
```c
// mandeljit.c
#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>
#include "micro-asm.h"
#define sqr(x) ((x) * (x))
typedef struct { double r; double i; } complex;
typedef void(*compiled)(complex*);
#define offsetof(type, field) ((unsigned long) &(((type *) 0)->field))
compiled compile(char *code) {
char *memory = mmap(NULL, 4096, PROT_READ | PROT_WRITE | PROT_EXEC,
MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
microasm a = { .dest = memory };
char src_dsp, dst_dsp;
char const r = offsetof(complex, r);
char const i = offsetof(complex, i);
for (; *code; code += 3) {
src_dsp = sizeof(complex) * (code[1] - 'a');
dst_dsp = sizeof(complex) * (code[2] - 'a');
switch (*code) {
case '=':
movpd_memory_reg(&a, src_dsp, xmm(0));
movpd_reg_memory(&a, xmm(0), dst_dsp);
break;
case '+':
movpd_memory_reg(&a, src_dsp, xmm(0));
addpd_memory_reg(&a, dst_dsp, xmm(0));
movpd_reg_memory(&a, xmm(0), dst_dsp);
break;
case '*':
movsd_memory_reg(&a, src_dsp + r, xmm(0));
movsd_memory_reg(&a, src_dsp + i, xmm(1));
movsd_memory_reg(&a, dst_dsp + r, xmm(2));
movsd_memory_reg(&a, dst_dsp + i, xmm(3));
movsd_reg_reg (&a, xmm(0), xmm(4));
mulsd (&a, xmm(2), xmm(4));
movsd_reg_reg (&a, xmm(1), xmm(5));
mulsd (&a, xmm(3), xmm(5));
subsd (&a, xmm(5), xmm(4));
movsd_reg_memory(&a, xmm(4), dst_dsp + r);
mulsd (&a, xmm(0), xmm(3));
mulsd (&a, xmm(1), xmm(2));
addsd (&a, xmm(3), xmm(2));
movsd_reg_memory(&a, xmm(2), dst_dsp + i);
break;
default:
fprintf(stderr, "undefined instruction %s (ASCII %x)\n", code, *code);
exit(1);
}
}
// Return to caller (important!)
asm_write(&a, 1, 0xc3);
return (compiled*) memory;
}
int main(int argc, char **argv) {
compiled fn = compile(argv[1]);
complex registers[4];
int i, x, y;
char line[1600];
printf("P5\n%d %d\n%d\n", 1600, 900, 255);
for (y = 0; y < 900; ++y) {
for (x = 0; x < 1600; ++x) {
registers[0].r = 2 * 1.6 * (x / 1600.0 - 0.5);
registers[0].i = 2 * 0.9 * (y / 900.0 - 0.5);
for (i = 1; i < 4; ++i) registers[i].r = registers[i].i = 0;
for (i = 0; i < 256 && sqr(registers[1].r) + sqr(registers[1].i) < 4; ++i)
(*fn)(registers);
line[x] = i;
}
fwrite(line, 1, sizeof(line), stdout);
}
return 0;
}
```

86
mandeljit.c Normal file
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@ -0,0 +1,86 @@
// mandeljit.c
#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>
#include "micro-asm.h"
#define sqr(x) ((x) * (x))
typedef struct { double r; double i; } complex;
typedef void(*compiled)(complex*);
#define offsetof(type, field) ((unsigned long) &(((type *) 0)->field))
compiled compile(char *code) {
char *memory = mmap(NULL, 4096, PROT_READ | PROT_WRITE | PROT_EXEC,
MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
microasm a = { .dest = memory };
char src_dsp, dst_dsp;
char const r = offsetof(complex, r);
char const i = offsetof(complex, i);
for (; *code; code += 3) {
src_dsp = sizeof(complex) * (code[1] - 'a');
dst_dsp = sizeof(complex) * (code[2] - 'a');
switch (*code) {
case '=':
movpd_memory_reg(&a, src_dsp, xmm(0));
movpd_reg_memory(&a, xmm(0), dst_dsp);
break;
case '+':
movpd_memory_reg(&a, src_dsp, xmm(0));
addpd_memory_reg(&a, dst_dsp, xmm(0));
movpd_reg_memory(&a, xmm(0), dst_dsp);
break;
case '*':
movsd_memory_reg(&a, src_dsp + r, xmm(0));
movsd_memory_reg(&a, src_dsp + i, xmm(1));
movsd_memory_reg(&a, dst_dsp + r, xmm(2));
movsd_memory_reg(&a, dst_dsp + i, xmm(3));
movsd_reg_reg (&a, xmm(0), xmm(4));
mulsd (&a, xmm(2), xmm(4));
movsd_reg_reg (&a, xmm(1), xmm(5));
mulsd (&a, xmm(3), xmm(5));
subsd (&a, xmm(5), xmm(4));
movsd_reg_memory(&a, xmm(4), dst_dsp + r);
mulsd (&a, xmm(0), xmm(3));
mulsd (&a, xmm(1), xmm(2));
addsd (&a, xmm(3), xmm(2));
movsd_reg_memory(&a, xmm(2), dst_dsp + i);
break;
default:
fprintf(stderr, "undefined instruction %s (ASCII %x)\n", code, *code);
exit(1);
}
}
// Return to caller (important!)
asm_write(&a, 1, 0xc3);
return (compiled*) memory;
}
int main(int argc, char **argv) {
compiled fn = compile(argv[1]);
complex registers[4];
int i, x, y;
char line[1600];
printf("P5\n%d %d\n%d\n", 1600, 900, 255);
for (y = 0; y < 900; ++y) {
for (x = 0; x < 1600; ++x) {
registers[0].r = 2 * 1.6 * (x / 1600.0 - 0.5);
registers[0].i = 2 * 0.9 * (y / 900.0 - 0.5);
for (i = 1; i < 4; ++i) registers[i].r = registers[i].i = 0;
for (i = 0; i < 256 && sqr(registers[1].r) + sqr(registers[1].i) < 4; ++i)
(*fn)(registers);
line[x] = i;
}
fwrite(line, 1, sizeof(line), stdout);
}
return 0;
}

43
micro-asm.h Normal file
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@ -0,0 +1,43 @@
// micro-asm.h
#include <stdarg.h>
typedef struct {
char *dest;
} microasm;
// this makes it more obvious what we're doing later on
#define xmm(n) (n)
void asm_write(microasm *a, int n, ...) {
va_list bytes;
int i;
va_start(bytes, n);
for (i = 0; i < n; ++i) *(a->dest++) = (char) va_arg(bytes, int);
va_end(bytes);
}
void movsd_reg_memory(microasm *a, char reg, char disp)
{ asm_write(a, 5, 0xf2, 0x0f, 0x11, 0x47 | reg << 3, disp); }
void movsd_memory_reg(microasm *a, char disp, char reg)
{ asm_write(a, 5, 0xf2, 0x0f, 0x10, 0x47 | reg << 3, disp); }
void movsd_reg_reg(microasm *a, char src, char dst)
{ asm_write(a, 4, 0xf2, 0x0f, 0x11, 0xc0 | src << 3 | dst); }
void mulsd(microasm *a, char src, char dst)
{ asm_write(a, 4, 0xf2, 0x0f, 0x59, 0xc0 | src << 3 | dst); }
void addsd(microasm *a, char src, char dst)
{ asm_write(a, 4, 0xf2, 0x0f, 0x58, 0xc0 | dst << 3 | src); }
void subsd(microasm *a, char src, char dst)
{ asm_write(a, 4, 0xf2, 0x0f, 0x5c, 0xc0 | dst << 3 | src); }
void movpd_reg_memory(microasm *a, char reg, char disp)
{ asm_write(a, 5, 0x66, 0x0f, 0x11, 0x47 | reg << 3, disp); }
void movpd_memory_reg(microasm *a, char disp, char reg)
{ asm_write(a, 5, 0x66, 0x0f, 0x10, 0x47 | reg << 3, disp); }
void addpd_memory_reg(microasm *a, char disp, char reg)
{ asm_write(a, 5, 0x66, 0x0f, 0x58, 0x47 | reg << 3, disp); }